Suggest Treatment For Severe Gastritis And Hypoglycemia

My 23 yr old son just returned from Bulgaria where he had a severe flare-up of gastritis which seemed to occur along with an attack of hypoglycemia due to not enough food available, exhaustion, too much flying and not eating during a film shoot. He s back in NYC now, still weak but much better. He has a crazy schedule of travel and work in spurts and I d like to know what he should do beginning about a day ahead of time, on the plane, during a shoot so that this doesn t happen again. Should he always have food with him? Should he make sure he eats something every few hours? He shoots in remote locations internationally. What would be the best types of bars and things to bring from home?